Essential Elements of Life About 25 of the 92 elements are
essential to life Carbon, hydrogen, oxygen, and nitrogen make up
96% of living matter Most of the remaining 4% consists of calcium,
phosphorus, potassium, and sulfur Trace elements are those required
by an organism in minute quantities Copyright 2008 Pearson
Education, Inc., publishing as Benjamin Cummings
Slide 3
Table 2-1
Slide 4
The formation and function of molecules depend on chemical
bonding between atoms Atoms with incomplete valence shells can
share or transfer valence electrons with certain other atoms These
interactions usually result in atoms staying close together, held
by attractions called chemical bonds Copyright 2008 Pearson
Education, Inc., publishing as Benjamin Cummings
Slide 5
Covalent Bonds A covalent bond is the sharing of a pair of
valence electrons by two atoms In a covalent bond, the shared
electrons count as part of each atoms valence shell Copyright 2008
Pearson Education, Inc., publishing as Benjamin Cummings
Slide 6
A molecule consists of two or more atoms held together by
covalent bonds A single covalent bond, or single bond, is the
sharing of one pair of valence electrons A double covalent bond, or
double bond, is the sharing of two pairs of valence electrons
Copyright 2008 Pearson Education, Inc., publishing as Benjamin
Cummings
Slide 7
Covalent bonds can form between atoms of the same element or
atoms of different elements A compound is a combination of two or
more different elements Bonding capacity is called the atoms
valence Copyright 2008 Pearson Education, Inc., publishing as
Benjamin Cummings
Slide 8
Electronegativity is an atoms attraction for the electrons in a
covalent bond The more electronegative an atom, the more strongly
it pulls shared electrons toward itself Copyright 2008 Pearson
Education, Inc., publishing as Benjamin Cummings
Slide 9
Ionic Bonds Atoms sometimes strip electrons from their bonding
partners An example is the transfer of an electron from sodium to
chlorine After the transfer of an electron, both atoms have charges
A charged atom (or molecule) is called an ion Copyright 2008
Pearson Education, Inc., publishing as Benjamin Cummings
Slide 10
Hydrogen Bonds A hydrogen bond forms when a hydrogen atom
covalently bonded to one electronegative atom is also attracted to
another electronegative atom In living cells, the electronegative
partners are usually oxygen or nitrogen atoms Copyright 2008
Pearson Education, Inc., publishing as Benjamin Cummings
Slide 11
Fig. 2-16 ++ ++ ++ ++ ++ Water (H 2 O) Ammonia (NH 3 ) Hydrogen
bond
Slide 12
Molecular Shape and Function A molecules shape is usually very
important to its function A molecules shape is determined by the
positions of its atoms valence orbitals In a covalent bond, the s
and p orbitals may hybridize, creating specific molecular shapes
Copyright 2008 Pearson Education, Inc., publishing as Benjamin
Cummings
Slide 13
Molecular Shape and Function A molecules shape is usually very
important to its function A molecules shape is determined by the
positions of its atoms valence orbitals In a covalent bond, the s
and p orbitals may hybridize, creating specific molecular shapes
Copyright 2008 Pearson Education, Inc., publishing as Benjamin
Cummings
Slide 14
Fig. 2-18 (a) Structures of endorphin and morphine (b) Binding
to endorphin receptors Natural endorphi n Endorphin receptors
Morphine Brain cell Morphine Natural endorphin Key Carbon Hydrogen
Nitroge n Sulfu r Oxygen
Slide 15
Fig. 2-18 (a) Structures of endorphin and morphine (b) Binding
to endorphin receptors Natural endorphi n Endorphin receptors
Morphine Brain cell Morphine Natural endorphin Key Carbon Hydrogen
Nitroge n Sulfu r Oxygen
Slide 16
Overview: The Molecule That Supports All of Life Water is the
biological medium on Earth All living organisms require water more
than any other substance Most cells are surrounded by water, and
cells themselves are about 7095% water The abundance of water is
the main reason the Earth is habitable Copyright 2008 Pearson
Education, Inc., publishing as Pearson Benjamin Cummings
Slide 17
Concept 3.1: The polarity of water molecules results in
hydrogen bonding The water molecule is a polar molecule: The
opposite ends have opposite charges Polarity allows water molecules
to form hydrogen bonds with each other Animation: Water Structure
Animation: Water Structure Copyright 2008 Pearson Education, Inc.,
publishing as Pearson Benjamin Cummings
Slide 18
Fig. 3-2 Hydrogen bond H + + H O + + + + + +
Slide 19
Concept 3.2: Four emergent properties of water contribute to
Earths fitness for life Four of waters properties that facilitate
an environment for life are: Cohesive behavior Ability to moderate
temperature Expansion upon freezing Versatility as a solvent
Copyright 2008 Pearson Education, Inc., publishing as Pearson
Benjamin Cummings
Slide 20
Cohesion Collectively, hydrogen bonds hold water molecules
together, a phenomenon called cohesion Cohesion helps the transport
of water against gravity in plants Adhesion is an attraction
between different substances, for example, between water and plant
cell walls Animation: Water Transport Animation: Water Transport
Copyright 2008 Pearson Education, Inc., publishing as Pearson
Benjamin Cummings
Slide 21
Fig. 3-3 Water-conducting cells Adhesion Cohesion 150 m
Direction of water movement
Slide 22
Surface tension is a measure of how hard it is to break the
surface of a liquid Surface tension is related to cohesion
Copyright 2008 Pearson Education, Inc., publishing as Pearson
Benjamin Cummings
Slide 23
Fig. 3-4
Slide 24
Moderation of Temperature Water absorbs heat from warmer air
and releases stored heat to cooler air Water can absorb or release
a large amount of heat with only a slight change in its own
temperature Copyright 2008 Pearson Education, Inc., publishing as
Pearson Benjamin Cummings
Slide 25
Heat and Temperature Kinetic energy is the energy of motion
Heat is a measure of the total amount of kinetic energy due to
molecular motion Temperature measures the intensity of heat due to
the average kinetic energy of molecules Copyright 2008 Pearson
Education, Inc., publishing as Pearson Benjamin Cummings
Slide 26
The Celsius scale is a measure of temperature using Celsius
degrees (C) A calorie (cal) is the amount of heat required to raise
the temperature of 1 g of water by 1C The calories on food packages
are actually kilocalories (kcal), where 1 kcal = 1,000 cal The
joule (J) is another unit of energy where 1 J = 0.239 cal, or 1 cal
= 4.184 J Copyright 2008 Pearson Education, Inc., publishing as
Pearson Benjamin Cummings
Slide 27
Waters High Specific Heat The specific heat of a substance is
the amount of heat that must be absorbed or lost for 1 g of that
substance to change its temperature by 1C The specific heat of
water is 1 cal/g/C Water resists changing its temperature because
of its high specific heat Copyright 2008 Pearson Education, Inc.,
publishing as Pearson Benjamin Cummings
Slide 28
Waters high specific heat can be traced to hydrogen bonding
Heat is absorbed when hydrogen bonds break Heat is released when
hydrogen bonds form The high specific heat of water minimizes
temperature fluctuations to within limits that permit life
Copyright 2008 Pearson Education, Inc., publishing as Pearson
Benjamin Cummings
Slide 29
Fig. 3-5 San Diego 72 40 miles Pacific Ocean 70s (F ) 80s 90s
100s Santa Barbara 73 Los Angeles (Airport) 75 Burbank 90 San
Bernardino 100 Riverside 96 Santa Ana 84 Palm Springs 106
Slide 30
Evaporative Cooling Evaporation is transformation of a
substance from liquid to gas Heat of vaporization is the heat a
liquid must absorb for 1 g to be converted to gas As a liquid
evaporates, its remaining surface cools, a process called
evaporative cooling Evaporative cooling of water helps stabilize
temperatures in organisms and bodies of water Copyright 2008
Pearson Education, Inc., publishing as Pearson Benjamin
Cummings
Slide 31
Insulation of Bodies of Water by Floating Ice Ice floats in
liquid water because hydrogen bonds in ice are more ordered, making
ice less dense Water reaches its greatest density at 4C If ice
sank, all bodies of water would eventually freeze solid, making
life impossible on Earth Copyright 2008 Pearson Education, Inc.,
publishing as Pearson Benjamin Cummings
Slide 32
Fig. 3-6 Hydrogen bond Liquid water Hydrogen bonds break and
re-form Ice Hydrogen bonds are stable
Slide 33
The Solvent of Life A solution is a liquid that is a
homogeneous mixture of substances A solvent is the dissolving agent
of a solution The solute is the substance that is dissolved An
aqueous solution is one in which water is the solvent Copyright
2008 Pearson Education, Inc., publishing as Pearson Benjamin
Cummings
Slide 34
Hydrophilic and Hydrophobic Substances A hydrophilic substance
is one that has an affinity for water A hydrophobic substance is
one that does not have an affinity for water Oil molecules are
hydrophobic because they have relatively nonpolar bonds A colloid
is a stable suspension of fine particles in a liquid Copyright 2008
Pearson Education, Inc., publishing as Pearson Benjamin
Cummings
Slide 35
Solute Concentration in Aqueous Solutions Most biochemical
reactions occur in water Chemical reactions depend on collisions of
molecules and therefore on the concentration of solutes in an
aqueous solution Copyright 2008 Pearson Education, Inc., publishing
as Pearson Benjamin Cummings
Slide 36
Molecular mass is the sum of all masses of all atoms in a
molecule Numbers of molecules are usually measured in moles, where
1 mole (mol) = 6.02 x 10 23 molecules Avogadros number and the unit
dalton were defined such that 6.02 x 10 23 daltons = 1 g Molarity
(M) is the number of moles of solute per liter of solution
Copyright 2008 Pearson Education, Inc., publishing as Pearson
Benjamin Cummings
Slide 37
Concept 3.3: Acidic and basic conditions affect living
organisms A hydrogen atom in a hydrogen bond between two water
molecules can shift from one to the other: The hydrogen atom leaves
its electron behind and is transferred as a proton, or hydrogen ion
(H + ) The molecule with the extra proton is now a hydronium ion (H
3 O + ), though it is often represented as H + The molecule that
lost the proton is now a hydroxide ion (OH ) Copyright 2008 Pearson
Education, Inc., publishing as Pearson Benjamin Cummings
Slide 38
Water is in a state of dynamic equilibrium in which water
molecules dissociate at the same rate at which they are being
reformed Copyright 2008 Pearson Education, Inc., publishing as
Pearson Benjamin Cummings
Slide 39
Fig. 3-UN2 Hydronium ion (H 3 O + ) Hydroxide ion (OH ) 2H 2 O
H H H H H H H H O O O O
Slide 40
Though statistically rare, the dissociation of water molecules
has a great effect on organisms Changes in concentrations of H +
and OH can drastically affect the chemistry of a cell Copyright
2008 Pearson Education, Inc., publishing as Pearson Benjamin
Cummings
Slide 41
Though statistically rare, the dissociation of water molecules
has a great effect on organisms Changes in concentrations of H +
and OH can drastically affect the chemistry of a cell Copyright
2008 Pearson Education, Inc., publishing as Pearson Benjamin
Cummings
Slide 42
Effects of Changes in pH Concentrations of H + and OH are equal
in pure water Adding certain solutes, called acids and bases,
modifies the concentrations of H + and OH Biologists use something
called the pH scale to describe whether a solution is acidic or
basic (the opposite of acidic) Copyright 2008 Pearson Education,
Inc., publishing as Pearson Benjamin Cummings
Slide 43
Acids and Bases An acid is any substance that increases the H +
concentration of a solution A base is any substance that reduces
the H + concentration of a solution Copyright 2008 Pearson
Education, Inc., publishing as Pearson Benjamin Cummings
Slide 44
The pH Scale In any aqueous solution at 25C the product of H +
and OH is constant and can be written as [H + ][OH ] = 10 14 The pH
of a solution is defined by the negative logarithm of H +
concentration, written as pH = log [H + ] For a neutral aqueous
solution [H + ] is 10 7 = (7) = 7 Copyright 2008 Pearson Education,
Inc., publishing as Pearson Benjamin Cummings
Slide 45
Acidic solutions have pH values less than 7 Basic solutions
have pH values greater than 7 Most biological fluids have pH values
in the range of 6 to 8 Copyright 2008 Pearson Education, Inc.,
publishing as Pearson Benjamin Cummings
Buffers The internal pH of most living cells must remain close
to pH 7 Buffers are substances that minimize changes in
concentrations of H + and OH in a solution Most buffers consist of
an acid-base pair that reversibly combines with H + Copyright 2008
Pearson Education, Inc., publishing as Pearson Benjamin
Cummings
Slide 48
Threats to Water Quality on Earth Acid precipitation refers to
rain, snow, or fog with a pH lower than 5.6 Acid precipitation is
caused mainly by the mixing of different pollutants with water in
the air and can fall at some distance from the source of pollutants
Acid precipitation can damage life in lakes and streams Effects of
acid precipitation on soil chemistry are contributing to the
decline of some forests Copyright 2008 Pearson Education, Inc.,
publishing as Pearson Benjamin Cummings
Slide 49
Fig. 3-10 More acidic 0 Acid rain Acid rain Normal rain More
basic 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Slide 50
Human activities such as burning fossil fuels threaten water
quality CO 2 is released by fossil fuel combustion and contributes
to: A warming of earth called the greenhouse effect Acidification
of the oceans; this leads to a decrease in the ability of corals to
form calcified reefs Copyright 2008 Pearson Education, Inc.,
publishing as Pearson Benjamin Cummings